Tissue ablation and assessment system and method of use thereof

ABSTRACT

The present disclosure provides a system with an innovative electrode designed as an RF/microwave antenna as well as methods to monitor/assess biological tissue and perform surgical procedures.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119(e)of U.S. Provisional Application Ser. No. 62/189,793, filed Jul. 8, 2015,U.S. Provisional Application Ser. No. 62/301,453, filed Feb. 29, 2016,and U.S. Provisional Application Ser. No. 62/341,071, filed May 25,2016, the entire contents of which are incorporated herein by referencein their entireties.

BACKGROUND OF THE DISCLOSURE Field of the Invention

The invention relates generally to medical devices and more specificallyto a system for tissue ablation and methods of use thereof.

Background Information

The electrical characteristics of an RF/microwave antenna in thefrequency domain e.g. reflection coefficient v/s frequency, are afunction of the antenna design, electrical properties (e.g.conductivity, relative permittivity, and the like) and the temperatureof the medium surrounding the antenna. During RF ablation procedures,the tissue properties including conductivity, permittivity, and tissuetemperature change significantly. These changes in the tissue can bemonitored by detecting the changes in frequency domain electricalproperties of antennas placed in direct contact with the tissue beingablated, and used to quantify extent of ablation and progression oflesion formation.

The characteristic electrical properties of an RF/microwave antenna inthe frequency domain (e.g. reflection coefficient or return loss v/sfrequency), as measured by a vector impedance network analyzer during areflection/S11 measurement, are a function of the antenna design,electrical properties of the medium (e.g. conductivity, permittivity,and the like) and temperature of the medium surrounding the antenna. Fora given antenna, the characteristic reflection electrical properties ofthe antenna, i.e. magnitude of impedance, return loss, reflectioncoefficient, phase angle, resonant frequency, and the like, will changein the frequency domain depending on the physical properties oftissue/medium surrounding the antenna. Thus monitoring the change incharacteristic reflection electrical properties of an antenna in thefrequency domain, the properties of the tissue/medium surrounding theantenna can be inferred via a S11 measurement on a frequency sweepvector network analyzer.

Similarly, transmission of electromagnetic waves between two antennas orcoupling of two antennas through a medium is a function of antennadesigns and electrical properties and temperature of the medium betweenthe two antennas. Monitoring the change in transmission characteristicbetween two antennas, as measured during a S21/S12 measurement, can beused to infer the change in electrical properties of the tissue betweenthe antennas.

The RF ablation processes changes the state of free or bound water inthe tissue and denatures cell membrane proteins, this changes dielectricrelaxation of proteins, cell membranes, and the like, resulting in achange in dielectric properties of the tissue. These changes betweenablated and non-ablated tissue should provide sufficient dielectriccontrast to distinguish extent of ablation by monitoring time domainreflection coefficient peaks of the electrode-antenna or monitoring thetransmission/coupling characteristics of two antennae Since themeasurements are carried out in a wide frequency range, and the tissuepenetration depth are different at various frequencies; ablated tissuethickness will influence electrical properties of the antenna-electrode(staying with convention which used later).

During RF ablation (RFA) procedures e.g. cardiac ablation, typically lowfrequency RF (300-700 KHz) is delivered into the tissue via theelectrode, resulting in ohmic heating of the tissue at the electrodetissue interface. The inventors propose to redesign the electrode of theRF ablation catheters/devices as a RF/microwave antenna or antennae andmeasure the electrical properties of the electrode antenna or antennaevia S11 and/or S21 measurements in real-time during ablation as a methodto monitor/assess extent of ablation/lesion formation. By detecting thechanges in the characteristic electrical properties of the antenna orantennae during the ablation process (which are in the high frequencyrange 1 MHz-4 GHz or higher), we can infer the changes in the electricalproperties of the tissue being ablated. Since the RF energy penetrationvaries with frequency, measurement of the antenna electrical propertiesin the frequency domain will enable infer tissue electrical propertiesalong the thickness, and monitoring changes in the time domain duringthe ablation process will enable infer ablation lesion extent, qualityand progression.

The electrical characteristics e.g. return loss v/s frequency of theantenna electrode is a function of the physical and electricalproperties of the tissue in vicinity of the antenna electrode. Theelectrical characteristics of the antenna electrode, i.e. time domainfrequency dips/peaks in return loss/reflection coefficient; are afunction of dielectric properties, e.g. conductivity, relativepermittivity and temperature of the tissue in contact. Thus changes tothe time domain frequency dips/peaks in return loss/reflection.Similarly, coupling or electromagnetic (EM) transmission characteristicchanges between two antennas can be used to infer changes in tissueproperties between two antennas.

Conventional ablation systems lack a significant capacity to accuratelyassess lesion formation and characterize tissue in real-time during anablation procedure. As such, there exists a need for an ablationcatheter system with an electrode designed as an RF/microwave antenna aswell as methods to monitor/assess lesion progression.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a system with an innovative electrodedesigned as an RF/microwave antenna as well as methods to monitor/assessbiological tissue and perform surgical procedures.

In one aspect, the disclosure provides an ablation device. The deviceincludes at least one antenna configured to transmit and receiveassessment signals having frequencies of at least 1 MHz to and fromtissue; and a high frequency output configured to output the receivedassessment signal to a network analyzer and signal processing device,wherein the at least one antenna is further configured to transmit anablation signal to the tissue.

In another aspect, the disclosure provides a device for assessing thestate of a biological tissue. The device includes at least one antennaconfigured to transmit and receive assessment signals having frequenciesof at least 1 MHz to and from tissue; and a high frequency outputconfigured to output the received assessment signal to a networkanalyzer and signal processing device.

In yet another aspect, the invention provides a system for assessing thestate of a biological tissue. The system includes a network analyzer andsignal processing device including a high frequency input configured toreceive a received assessment signal from tissue via a catheter, thereceived assessment signal having a frequency of at least 1 MHz; and aprocessor configured to detect an electrical property of the receivedassessment signal and determine a property of the tissue based on thedetected electrical property of the received assessment signal.

In still another aspect, the disclosure provides a method fordetermining a property of a tissue. The method includes:

transmitting, with at least one antenna of a catheter, a transmittedassessment signal having a frequency of at least 1 MHz to tissue;

receiving, with the at least one antenna, a received assessment signalhaving a frequency of at least 1 MHz from the tissue;

detecting, with a processor of a network analyzer and signal processingdevice, an electrical property of the received assessment signal; and

determining, with the processor, a property of the tissue based on thedetected electrical property of the received assessment signal.

In yet another aspect, the invention provides a method of performing asurgical procedure using the device of the disclosure. In embodiments,the procedure includes ablation of tissue.

These and other embodiments are described in greater detail below, inreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration depicting a conventional cardiac RF ablationcatheter and electrode as well as anatomic representations of anablation catheter in cardiac tissue and use on a patient.

FIG. 2A is a schematic view of an antenna electrode in one embodiment ofthe invention.

FIG. 2B is a cross-sectional view of the antenna electrode of FIG. 2A.

FIG. 2C is a graphic showing data generated using the antenna electrodeof FIG. 2A.

FIG. 3 is an illustration of an antenna electrode incorporated into asteerable catheter in one embodiment of the invention.

FIG. 4A is a cross-sectional view of a coaxial sensor on oneconfiguration.

FIG. 4B is a cross-sectional view of a coaxial sensor on oneconfiguration.

FIG. 4C is a cross-sectional view of a coaxial sensor on oneconfiguration.

FIG. 4D is a graph illustrating a return loss versus frequency profilegenerated via the sensor of FIG. 4B.

FIG. 5A is a schematic view of a spiral antenna electrode in oneembodiment of the invention.

FIG. 5B is a graph illustrating a return loss versus frequency profilegenerated via the antenna of FIG. 5A.

FIG. 6 is an illustration showing the layout of an experimental setupused to evaluate lesion assessment performance of an antenna electrodecatheter of the invention in an animal.

FIG. 7 is an illustration showing the layout of an ablation lesionassessment system of the invention for performing intracardiac ablationprocedures.

FIG. 8A is a graph illustrating a return loss versus frequency profile.

FIG. 8B is a graph illustrating a return loss versus frequency profile.

FIG. 8C is a graph illustrating a return loss versus frequency profile.

FIG. 9A is a graph illustrating a return loss versus frequency profile.

FIG. 9B is a graph illustrating a return loss versus frequency profile.

FIG. 9C is a graph illustrating a return loss versus frequency profile.

FIG. 10A is a graph illustrating a return loss versus frequency profile.

FIG. 10B is a graph illustrating a return loss versus frequency profile.

FIG. 11A is a graph illustrating a return loss versus frequency profile.

FIG. 11B is a graph illustrating a return loss versus frequency profile.

FIG. 11C is a graph illustrating a return loss versus frequency profile.

FIG. 11D is a graph illustrating a return loss versus frequency profile.

FIG. 11E is a graph illustrating a return loss versus frequency profile.

FIG. 12 is a graph illustrating the relationship between phase reversalfrequency/resonant frequency and lesion depth.

FIG. 13 is an illustration showing a user interface for monitoring anablation procedure using the system of the invention.

FIG. 14A is a schematic view of an ablation needle electrode in oneembodiment of the invention.

FIG. 14B is a cross-sectional view the electrode of FIG. 14A along lineA-A′.

FIG. 14C is an expanded view of the tip of the ablation needle electrodeof FIG. 14A.

FIG. 15A is a schematic view of an ablation needle electrode in oneembodiment of the invention.

FIG. 15B is an expanded view of the tip of the ablation needle electrodeof FIG. 15A.

FIG. 15C is a schematic view of the ablation needle electrode of FIG.15A inserted in tissue in one embodiment of the invention.

FIG. 15D is a schematic view of the ablation needle electrode of FIG.15A inserted in tissue in one embodiment of the invention.

FIG. 16A is a schematic view of an ablation needle electrode in oneembodiment of the invention.

FIG. 16B is a schematic view of the ablation needle electrode of FIG.16A inserted in tissue in one embodiment of the invention.

FIG. 17 is an illustration showing the layout of an ablation lesionassessment system of the invention.

FIG. 18 is an illustration showing the layout of an ablation lesionassessment system of the invention.

FIG. 19A is a schematic view of an ablation needle electrode in oneembodiment of the invention inserted into tissue in an RFA procedure.

FIG. 19B is a schematic view of an ablation needle electrode in oneembodiment of the invention inserted into tissue in an RFA procedure.

FIG. 19C is a schematic view of an ablation needle electrode in oneembodiment of the invention inserted into tissue in an RFA procedurecoupled with additional components of the system of the invention.

FIG. 20 is a set of graphs depicting data generated using the system ofthe invention.

FIG. 21 is an illustration showing the layout of an ablation lesionassessment system of the invention.

FIG. 22A is a schematic view of an antenna configuration which may beutilized in the needle electrode of the invention in one embodiment.

FIG. 22B is a schematic view of an antenna configuration which may beutilized in the needle electrode of the invention in one embodiment.

FIG. 22C is a schematic view of an antenna configuration which may beutilized in the needle electrode of the invention in one embodiment.

FIG. 22D is a schematic view of an antenna configuration which may beutilized in the needle electrode of the invention in one embodiment.

FIG. 22E is a schematic view of an antenna configuration which may beutilized in the needle electrode of the invention in one embodiment.

FIG. 22F is a schematic view of an antenna configuration which may beutilized in the needle electrode of the invention in one embodiment.

FIG. 23A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 23B is a schematic view of the antenna electrode of FIG. 23A.

FIG. 23C is a schematic view of the antenna electrode of FIG. 23A.

FIG. 23D is an expanded view of the tip of the antenna electrode of FIG.23A.

FIG. 24A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 24B is a schematic view of the antenna electrode of FIG. 23A.

FIG. 24C is an expanded view of the tip of the antenna electrode of FIG.23A.

FIG. 25A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 25B is a schematic view of the antenna electrode of FIG. 25A.

FIG. 26A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 26B is a schematic view of the antenna electrode of FIG. 26A.

FIG. 27A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 27B is a schematic view of the antenna electrode of FIG. 27A.

FIG. 27C is a schematic view of the antenna electrode of FIG. 27A.

FIG. 27D is a schematic view of the antenna electrode of FIG. 27A.

FIG. 27E is an expanded view of the tip of the antenna electrode of FIG.27A.

FIG. 28A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 28B is a schematic view of the antenna electrode of FIG. 28A.

FIG. 29A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 29B is a schematic view of the antenna electrode of FIG. 29A.

FIG. 29C is a schematic view of the antenna electrode of FIG. 29A.

FIG. 30A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 30B is a schematic view of the antenna electrode of FIG. 30A.

FIG. 31A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 31B is a schematic view of the antenna electrode of FIG. 31A.

FIG. 31C is a schematic view of the antenna electrode of FIG. 31A.

FIG. 32A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 32B is a schematic view of the antenna electrode of FIG. 32A.

FIG. 32C is a cross-sectional view of the antenna electrode of FIG. 31Aalong line A-A′.

FIG. 33A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 33B is a schematic view of the antenna electrode of FIG. 33A.

FIG. 34A is a schematic view of an antenna electrode in one embodimentof the invention.

FIG. 34B is a schematic view of the antenna electrode of FIG. 34A.

FIG. 35 is a schematic view of an ablation system in one embodiment ofthe invention.

FIG. 36 is a schematic view of an ablation system having a distallydisposed balloon in one embodiment of the invention.

FIG. 37 is an illustration depicting an ablation system in oneembodiment of the invention.

FIG. 38 is a schematic view of a portion of an ablation system in oneembodiment of the invention which includes a metal braided catheter.

FIG. 39 is an illustration depicting an ablation system in oneembodiment of the invention.

FIG. 40 is an illustration depicting an ablation system in oneembodiment of the invention.

FIG. 41 is an illustration depicting an ablation system in oneembodiment of the invention.

FIG. 42 is an illustration depicting an ablation system in oneembodiment of the invention.

DETAILED DESCRIPTION OF THE DISCLOSURE

In one aspect, the present disclosure provides a system for assessmentof biological tissue by measuring/monitoring characteristics ofelectromagnetic radiation on biological tissue. The includes a devicehaving at least one antenna configured to transmit and receiveassessment signals having frequencies of at least 1 MHz to and fromtissue; and a high frequency output configured to output the receivedassessment signal to a network analyzer and signal processing device.

In one embodiment the system is an ablation lesion assessment system. Inembodiments, the system includes an RF ablation catheter with an antennaelectrode, and optionally a vector network analyzer connected to theantenna electrode to enable reflection transmission measurements in afrequency range, i.e. S parameter measurements (S11 and S21/S12), dataacquisition and an analysis interface which predicts extent oftissue-electrode contact and lesion progression in real-time isdescribed.

In addition to measuring endocardial potential and delivering ablationRF (300-900 KHz range), the electrode of the RF ablation catheter isdesigned to have an additional functionality of an RF/microwave antenna.This enables the electrode to transmit and receive electromagneticenergy/frequencies in DC to GHz frequency range to the tissue beingablated, thus transmitting ablation energy at 100-700 KHz, sensingendocardial potential, as well as measuring S parameters in the KHz-GHzfrequency range.

The present disclosure provides various embodiments of the antennaelectrode of the invention. In various embodiments, the antennaelectrode is described as being incorporated in various devices, suchas, RF ablation catheters, microwave ablation catheters, intramyocardialinjection catheters, thermoacoustic imaging catheters, magneticresonance imaging (MRI) catheters which enable delivery of ablationenergy and transmission/receiving of MR signals, all of which have theability to enable monitor lesion assessment in real-time. However, thedevice of the invention need not be configured to ablate tissue butrather solely monitor the state of biological tissue.

This disclosure is intended to cover any adaptations or variations ofthe exemplary embodiment(s). In addition, in this disclosure, the terms“comprise” or “comprising” do not exclude other elements or steps, theterms “a” or “one” do not exclude a plural number, and the term “or”means either or both. Furthermore, characteristics or steps which havebeen described may also be used in combination with othercharacteristics or steps and in any order unless the disclosure orcontext suggests otherwise. References to “the method” includes one ormore methods, and/or steps of the type described herein which willbecome apparent to those persons skilled in the art upon reading thisdisclosure and so forth.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the invention, the preferred methods andmaterials are now described.

FIG. 1 illustrates a conventional steerable cardiac RF ablation catheterwith the ablation electrode at the distal end and handle at the proximalend. During an intracardiac RF ablation procedure for treatment ofcardiac arrhythmias, an ablation catheter is introduced in the cardiacchamber via the venous approach and a ground pad is placed on the skinto complete the RF circuit. The ablation electrode is placed in contactwith the cardiac tissue to be ablated and RF energy is delivered to thetissue to be ablated. Passage of a high frequency alternating currentinto the tissue causes local thermal injury, killing the tissue incontact with the electrode to create an ablation lesion, which resultsin conduction blocks. To ensure controlled thermal injury to themyocardial tissue, the ablation electrode needs to be in good electricalcontact with the myocardial tissue and the ablation procedure needs tobe monitored till desired depth of tissue is ablated. To monitor thecardiac ablation procedure, the inventors have redesigned the ablationelectrode of the cardiac ablation catheter as a RF/microwave antenna.The reflection transmission electrical properties of the antennaelectrode of the disclosure in the frequency domain during the durationof the ablation procedure is assessed to monitor procedure parametersand assess lesion formation, i.e., confirm electrode-tissue contact,confirm RF energy delivery to tissue, and confirm and assess lesionformation, i.e. depth of the lesion/tissue ablated, rate of ablation toensure safe ablation and avoid excessive RF ablation.

FIG. 2A is a schematic of an antenna electrode 10 in one embodiment ofthe invention where the antenna electrode is a spiral antenna electrode40. The spiral antenna electrode has a spiral positive plane 15 which isa helical spiral with each spiral separated by a dielectric 30. Thepositive spiral 15 is surrounded by a ground plane 20 separated by adielectric 30. FIG. 2B shows a schematic of the spiral antenna electrode40 on a tissue 1000 and electromagnetic model of tissue being ablated.FIG. 2C shows characteristic return loss 300 and phase angle 310response in the frequency domain from 85 MHz to 2 GHz in a physiologicalsaline solution using antenna electrode 10. Note the 180° phase shiftthat occurs at the resonant frequencies 320 at 350 MHz and 1000 MHz. Asthe dielectric properties of the medium surrounding the antenna changes,the return loss and phase angle profiles in the frequency domain change,and the resonant frequencies change as well. White arrows indicate thedirection of shift in resonant frequencies as the dielectric propertiesof the medium change. By monitoring the return loss, phase angleprofiles of the antenna electrode in the frequency domain and changes inresonant frequencies during the ablation procedures, the procedureparameters can be inferred and lesion formation can be monitored andassessed.

FIG. 3 illustrates a prototype spiral antenna electrode 40 incorporatedinto a steerable catheter 70 for performing percutaneous intracardiac RFablations. The distal deflectable section and spiral antenna sensorelectrode are shown in the inset. A coaxial cable 50 runs along thelength of the catheter 70 and connects to the interface circuitincluding low pass filters, high pass filters, RF generator and vectorimpedance network analyzer, to simultaneously deliver high frequencysensing signals (MHz-GHz) to and from the antenna electrode and lowfrequency ablation RF (KHz) to the tissue via the electrode, and a verylow frequency (DC) endomyocardial electrogram (EEG) signal from themyocardium to the EEG recording system.

The antenna electrode of the invention is configured to output energythat ablates tissue. The terms “ablate” or “ablation”, includingderivatives thereof, include, without limitation, substantial alteringof electrical properties, mechanical properties, chemical properties orother properties of tissue. The term electrode within the context of“antenna electrode” includes a discrete element, such as an electrode,or a plurality of discrete elements, such as a plurality of spaced apartelectrodes, which are positioned so as to collectively treat a region oftissue or discrete sites. One embodiment of an antenna electrode emitsenergy that ablates tissue, i.e., cardiac tissue, when the element iscoupled to and energized by an energy source. Examples of energyemitting ablation electrodes include, without limitation, electrodeelements coupled to direct current (DC) sources or alternating current(AC) sources (e.g., radiofrequency, RF, current sources), antennaelements energizable by microwave energy sources, pulsed high voltagesources, heating elements (e.g., metallic elements or other thermalconductors which are energized to emit heat via convective heattransfer, conductive heat transfer, and the like), light emittingelements (e.g., fiber optics capable of transmitting light sufficient toablate tissue when the fiber optics are coupled to a light source),light sources (e.g., lasers, light emitting diodes, and the like),ultrasonic elements such as ultrasound transducers adapted to emitultrasound waves sufficient to ablate tissue when coupled to suitableexcitation sources), combinations thereof and the like.

As used herein, the term “ablate,” including variations thereof, isconstrued to include, without limitation, to destroy or to permanentlydamage, injure, or traumatize tissue. For example, ablation may includelocalized tissue destruction, cell lysis, cell size reduction, necrosis,or combinations thereof.

In some embodiments, the ablation device may be connected to an energygenerator (e.g., RF) by electrical conductors within the shaft of theablation device or otherwise incorporated into the ablation system. RFenergy may be outputted to a desired frequency based on the treatment.Example frequencies include, without limitation, frequencies in therange of about 50 kHz to about 1000 MHz (e.g., 300 to 700 kHz). When theRF energy is directed into tissue, the energy is converted within thetissue into heat allowing the temperature of the tissue to be increased,for example to a range of 40° C. to about 99° C. In some embodiments, atemperature sensor may be used to monitor the temperature of the targettissue to confirm therapeutic delivery of RF. A temperature sensor mayalso be used to monitor temperature of non-target tissue to reduce oravoid iatrogenic injury.

While the device of the antenna electrode of the invention is describedgenerally with reference to use of RF, the antenna electrode describedherein can be used for Microwave Radiometry applications and thereformay be connected to an energy generator that generates microwave energy,e.g., energy having a frequency of between about 300 MHz and 300 GHz.

In some embodiments the ablation electrode may be an RF electrode inmonopolar configuration with a dispersive grounding pad on the patient'sskin to complete the electrical circuit. In other embodiments, theconfiguration of the RF electrode may be bipolar. Ablation energy may beradiofrequency electrical current having a frequency up to 1 MHz, 50 MHzor 100 MHz or in a range of about 300 to 1 MHz or about 300 to 700 kHzand a power in a range of about 1 to 50 W. The delivery of RF energy maybe controlled by an energy generator associated with a controller thatuses temperature feedback from a sensor associated with the system. Insome embodiments the antenna electrode functions to emit a substance asan ablation agent. In such embodiments the system may further comprise ameans to inject the substance such as a manually operated syringe orautomatically controlled pump. The emitted substance may be saline,phenol, ethanol, botulinum toxin or other neurotoxins, anesthetic agent,including but not limited to depolarizing or non-depolarizing agents,such as marcaine, bupivacaine, lidocaine, or other anesthetic agents,and other agents capable of reducing nerve signal transmission.

FIGS. 4A-C provide schematics of various configuration of coaxialsensors. Schematics shown in FIG. 4A and B depict positive plane 15 andcircular ground plane 20 of the coaxial sensor separated by dielectric30. The surface areas of the positive plane, ground plane and theseparation between them can be varied which affects the return losscharacteristics in the frequency domain. FIG. 4C shows a coaxial sensorwith an intermediate floating plane 25 which is not connected to either.FIG. 4D shows characteristic return loss versus frequency profiles forthe coaxial antenna sensor electrode of FIG. 4B in saline solutions ofconcentrations ranging from DI water to 1.1% saline. No distinctresonant frequencies can be seen, making it difficult to implement thisdesign in an antenna electrode configuration.

FIG. 5A is a schematic of a spiral antenna electrode 40 with a spiralpositive plane 15 where each strut is separated by a dielectric 30 andsurrounded by a ground plane 20; again separating the ground plane andthe spiral is a dielectric. The spiral acts as an inductor and the straycapacitance between the struts and between the positive plane and theground plane, results in giving this antenna a characteristic returnloss profile with a resonant frequency. FIG. 5B shows the return lossversus frequency profiles for the spiral antenna electrode 40 in salinesolutions of concentrations ranging from DI water to 1.1% saline. Thespiral antenna electrode of this design has a distinct resonantfrequency at about 1400 MHz for all concentrations of saline solution.However, as the saline concentration increases the return loss decreasesat lower frequencies; particularly between 10-500 MHz. The spiralantenna electrode's reflection properties in the frequency domain are afunction of electrical properties of the medium, i.e. conductivity andpermittivity of the medium can be used to monitor RF ablation proceduresand assess lesion formation in embodiments of the invention.

FIG. 6 shows the schematic setup of the system of the invention used toevaluate ablation lesion assessment performance of an antenna electrodedisposed in a catheter in an animal.

FIG. 7 show the schematic of the RF ablation lesion assessment system ofthe invention for performing intracardiac RF ablation procedures. Theablation RF generator provides ablation RF energy in the 1 KHz to 1 MHzrange. The network analyzer measures the reflection electricalproperties of the antenna electrode in MHz and GHz ranges. Interfacecircuit comprises a low pass and a high pass filter. The output of theRF generator passes thru a RF low pass filter or a band pass filter toallow only the ablation frequencies to pass through and attenuates allother frequencies by over 40 dB, thus preventing transmittingfrequencies which interfere with high frequency network analyzer signalsand measurements. The input and output of the network analyzer passesthru a high pass filter or a suitable band stop filter, which attenuatesthe ablating frequency by over 40 dB thus preventing any damage to thesensing hardware and has minimal insertion loss at all otherfrequencies. The vector network analyzer sends an incident signal to theantenna electrode in the MHz-GHz frequency range; the difference inamplitude and phase of the transmitted and reflected signals are used tocompute the return loss and phase angle properties of the antennaelectrode in the frequency domain. These are processed and recorded viaa computer or other hardware, and displayed during clinical use tomonitor the procedure and assess and monitor lesion formation.

In various embodiments, the system includes a low pass and high passfilter which may be band pass/band stop filters and an RF generator thathas a range of about 10 Hz to 100 MHz.

FIG. 8 shows the return loss and phase angle responses of the spiralantenna electrode 40 in the frequency domain when in blood (FIG. 8A), incontact with epicardial tissue (FIG. 8B) and in contact with fattytissue section on the epicardium (FIG. 8C). During clinical use thecatheter with the antenna electrode 40 is advanced in the cardiacchambers. When the electrode is in blood, the characteristic return lossprofile 300, phase angle profile 310, and resonant frequency 320, at˜325 Hz, as shown in FIG. 8A, are dependent on antenna electrode designand can change from one design to another. Depending on extent of tissuecontact and orientation of contact; this changes as shown in FIG. 8Bwith a flattening of the return loss profile 300 and shift in resonantfrequency 320 to about ˜400 MHz. Depending on the nature of tissue, i.e.fatty or ablated tissue or scar tissue, further increase in resonantfrequency might be exhibited.

FIG. 9 shows return loss, phase angle characteristic of the antennaelectrode 40 in a wider frequency range, i.e. 100 MHz to 2 GHz. In thisfrequency range two distinct resonant frequencies can be observed.Extent of electrode tissue contact may be assessed using one or moreresonant frequencies 320, e.g. at ˜350 MHz and 1200 MHz (FIG. 9A) whenthe electrode is in blood or saline, which then shifts to 400 and 1500MHz (FIG. 9) depending on extent of electrode-tissue contact. If theelectrode is fully in contact with ablated tissue, the resonantfrequency 320 may shift to 525 and 1700 MHz (FIG. 9C). The shift inresonant frequency from antenna-electrode in blood, to antenna-electrodeon tissue can be used to determine the antenna-electrode surface area incontact with tissue.

During the ablation procedure, it is important to maintain goodelectrode contact with tissue to ensure RF energy deposition in thetissue. With a moving heart wall this can be difficult and it isimportant for the physician to confirm RF energy deposition in thetissue. The antenna electrode 40 shows characteristic return loss andphase angle profiles when RF energy delivery is in blood. FIG. 10A showsa return loss and phase angle profile when antenna electrode is in bloodand 10B shows the same when ablation RF is turned on (with electrode inblood). When the electrode is in blood, the phase anglereversal/resonant frequency is ˜325 MHz (FIG. 10A); when RF ablation isturned on, this phase angle reversal/resonant frequency drops to ˜200MHz and stays there. This distinct characteristic return loss 300, phaseangle 310 and resonant frequency 320 response (FIG. 10B) when RF energyis delivered in blood notifies the physician of the loss ofelectrode-tissue contact.

With reference to FIG. 11, progression of lesion formation is indicatedby the return loss profiles 300 and phase angle profiles 310 in thefrequency domain at different time points in the ablation procedure.When RF energy deposition in tissue is translated into tissuetemperature rise and thermal tissue damage, an ablation lesion iscreated. This lesion formation process can be discerned by monitoringreturn loss profiles 300, phase angle profiles 310 and phase reversalfrequencies 320 in the frequency domain during the ablation procedure(FIGS. 11A-E). The return loss 300 profile is flat when the electrode isin contact with tissue and phase reversal frequency is ˜400 MHz (FIG.11A), on onset of RF ablation phase reversal frequency 320 drops to 250MHz and a dip in return loss 300 is seen at ˜200 MHz (FIG. 11B); asablation progresses phase reversal frequency 320 increases gradually to400, 600 and steadies at 800 MHz for this antenna electrode design(FIGS. 11C-E). By monitoring the change in phase reversal frequency 320and return loss profiles 300, thermal tissue damage can be confirmed.Thus, the return loss profile 300, phase angle profile 310 and resonantfrequency/phase reversal frequency 320 can be used to inferelectrode-tissue contact, confirm RF energy delivery to the wall andassess lesion formation.

FIG. 12 shows the relationship between phase reversal frequency/resonantfrequency 320 and lesion depth. The resonant frequency/phase reversalfrequency 320 observed during RF ablation procedure correlates to thedepth of the lesion formed (FIG. 12) and the nature of the surface ofthe lesion. The phase reversal frequency observed during ablation can beused to estimate lesion depth under optimized conditions of saline flushirrigation, applied power and estimated electrode-tissue contact surfacearea. This methodology of using the return loss profiles 300, phaseangle profile 310 of the antenna electrode to infer lesion depth can beimplemented clinically to monitor and assess lesion formation in thesystem of the invention.

As it can be evidenced FIGS. 8-12 the return loss profile 300, the phaseangle profile 320, the resonant frequency/phase angle reversal frequency320 of the antenna electrode can be used to monitor cardiac RF ablationprocedure parameters e.g. confirm and quantify electrode tissue contact,confirm RF energy deposition in blood, confirm lesion formation andassess lesion depth during the procedure. In a typical intracardiacablation procedure the RF ablation catheter with the antenna electrodeof the invention is advanced in the cardiac chambers using x-rayfluoroscopy guidance, with preoperative CT or MRI images. A baselinereturn loss, phase angle, resonant frequency data set is obtained withthe antenna electrode in blood. Then the antenna electrode is contactedto the cardiac tissue in different orientations to get another baselinereturn loss, phase angle and resonant frequency data set with antennaelectrode in contact with tissue. With the baseline data acquired andproperties recorded, the physician gets the information on the returnloss, phase angle and resonant frequencies that are needed to confirmcontact and to quantify the extent of electrode-tissue contact i.e.surface area of electrode in contact with tissue. The ablation catheteris then steered to the anatomical region of interest to be ablated.Using the baseline data when antenna electrode was in blood and tissue,the physician confirms electrode-tissue contact, adjusts the catheter tomaximize the contact; and delivers the ablation current into the tissue.Monitoring the resonant frequency changes, ensures that theelectrode-tissue contact is maintained for the duration of ablation. Bymonitoring the resonant frequency progression, lesion formation isconfirmed and ablation is stopped when resonant frequency reaches adesired set-point indicative of the lesion depth required at ablationlocation. Thus the RF ablation lesion assessment system of the inventionincluding an ablation catheter with an antenna electrode, can be used tomonitor cardiac RF ablation procedure and assess lesion formation bymonitoring the reflection characteristics in the frequency domain via avector network analyzer.

The purpose of the cardiac RF ablation procedure is to create apermanent conduction block. To achieve this it is important to ablatethe entire wall thickness of the atria or ventricle safely, i.e. noexcessive power during ablation which will cause steam pops or excessiveduration of ablation which may cause perforation. To enable this, the RFenergy input needs to be closely regulated throughout the procedure andelectrode tissue-contact needs to be maintained. RF ablation primarilyoccurs by ohmic heating, where the tissue in contact with the electrodeheats due to the current which passes thru it. This heat is thenconducted deeper in the tissue, creating a deeper lesion. If the localtissue impedance rises significantly higher e.g. when tissue is charred,the RF power delivered by the electrode in the tissue is not effectivelyconverted to heat and superficial lesions are created. For betterclinical outcomes entire wall thickness of the atria needs to beablated, e.g. 3-4 mm. To achieve this, local tissue impedance andtemperature needs to be regulated at an optimum level i.e. the amplitudeof power applied needs to be regulated. The rate of change of phasereversal (from 400 MHz to 250 MHz back to 400 MHz and higher) observedduring the ablation procedure is a measure of the impedance of thetissue in contact with the electrode; to make deeper lesions the powerlevel/wattage of RF deposition in the tissue and can be adjusted to holdthe phase reversal frequency steady at 400-600 MHz by regulating thepower applied. Thus deeper lesions can be created without causingexcessive tissue heating, which results in surface charring or steampops. Since the resonant frequency is held constant between a certainfrequency range, resonant frequency alone cannot be used to assesslesion depth. Since lesion depth is also directly proportional to thetotal energy deposited in the tissue, the total power applied during theentire procedure or the total power applied when the resonant frequencywas held constant in the selected frequency range, e.g. 400-600 MHz, maybe used to estimate the lesion depth.

The complications during the procedure are caused by excessive ablation,i.e. excessively longer duration of ablation and/or by applyingexcessively high power. The rate of resonant frequency change during RFablation is an indication of the dielectric properties change andtemperature of the tissue in contact with the electrode. During theablation procedure, there is a significant change in resonant frequencyas ablation progresses, and the rate of resonant frequency/phasereversal frequency change is an indication of the rate of change oftissue electrical properties and tissue temperature; which is also ameasure of amplitude of power applied. To create deeper lesions safely,the power input rate needs to be titrated which can be accomplished by acontroller which monitors the rate of resonant frequency change andaccordingly adjusts the power input. Alternately, the power input can beadjusted manually to maintain an optimum resonant frequency change rate.

The objective of the cardiac ablation procedure for treatment of complexarrhythmias e.g. atrial fibrillation, is to create contiguous transmurallesions within anatomical boundaries, e.g. around pulmonary vein ostia.The methods described earlier disclose using the RF ablation lesionassessment system of the invention to create lesions of known depths,thus transmural lesions may be created. To create contiguous lesions,the antenna electrode catheter needs to differentiate between ablatedtissue and non-ablated tissue. In FIG. 9, the distinctly differentreturn loss, phase angle and resonant frequency characteristics of theantenna electrode when in contact with blood, tissue and ablated tissueare shown. This feature can be used to identify the tissue type incontact with the catheter. This can be done in a clinical setting bysteering the catheter to different points to create electrode-tissuecontact, monitoring its return loss phase angle profiles and phasereversal/resonant frequencies to assess tissue type. The RF ablationlesion assessment system may be configured to have two modes, assessmentmode and the ablation mode. Since adding RF filters in line will causeadded electromagnetic system noise, a switch in the system will enabletaking the filters off line and having the catheter directly connectedto the network analyzer. The frequency range and amplitude ofassessment/sensing signal could be higher for the purpose of assessmentas well. The operator will have the option to select the modes; however,when ablation RF is turned on, the system will have an auto switch toablation mode. To enable tissue assessment, the physician selects theassessment mode then obtains baseline data of return loss, phase angleand resonant frequency characteristics when the electrode is in blood,and contacting known healthy tissue in different orientations. Once thisis done, the catheter is steered to the desired anatomical targets andreturn loss, phase angle, resonant frequency, and the like, propertiesare recorded; compared to the baseline data to infer tissue type incontact. The system can switch between assessment and ablation modeswith a switch; or the ablation mode automatically engages when the RFswitch is turned on.

FIG. 13 shows a graphical user interface which can be used to monitorablation procedures and assess lesion formation. A suitable userinterface indicates the different procedure parameters, i.e. area oftissue electrode contact, and the type of tissue in contact withelectrode. Additionally, during RF ablation it includes an indicationconfirming RF deposition in tissue and assessment of lesion formation,i.e. rate of lesion formation and depth of lesion formation.Baseline/Benchmark assessment of different contact conditions are madeprior to start of the procedure, e.g. electrode in blood, electrode incontact with tissue in different orientation, and the like. Beforeablation, assessing the tissue type as ablated tissue, non-ablatedtissue, blood, fatty tissue will be required. This will be done in theassessment mode. These can be indicated as a slide bar/graph withmarkings for blood, tissue, ablated tissue, and lesion depth are made onthe scale, a sliding cursor/arrow indicates the position of theelectrode at a given time. Area of electrode in contact with tissuebefore and during RF ablation needs to be continuously indicated. Thiscan be the actual surface area, % of the area, and the like. Duringablation, rate of RF input in terms applied wattage and saline flushrate may be entered in the system for estimating lesion depth and totalpower input. During the ablation process the rate of RF deposition intissue will be displayed and quantified. This will be estimated on thetotal wattage applied, saline flush rate and shift in resonant frequencyobserved. Lesion progression will be displayed as an estimated lesiondepth based on resonant frequency and total power deposited (asestimated from the electrode area in contact, saline flush rate andapplied watts). Alerts indicating excessive ablation rate and unsafesurface conditions which will cause steam pops can be included.

Besides cardiac ablation, RF ablation is used for treatment of otherclinical conditions e.g., nerve ablation for pain management, livercancer tumor ablation, breast cancer tumor ablation, and the like. Inthese procedures a needle electrode/probe/device is placed in the tissueto be ablated using X-ray, ultrasound, CT or MRI guidance, it is thenconnected to the RF generator, a grounding pad is placed on the patient.RF wattage and time duration of RF application is based on physicianexperience and manufacturer provided estimates of ablation zone undergiven ablation conditions. The ablation needle-electrodes can bedesigned as RF/microwave antennae, and by monitoring the change inreflection transmission electrical properties in the frequency domainduring the procedure enable infer ablation zone and extent of thermalinjury. Devices and methods to intraoperatively access RF ablationzone/lesion, extent of thermal tissue damage and maximize ablation zoneare described and included in the invention.

FIG. 14 shows the schematic of the RF ablation needle electrode of theinvention as a modified dipole/monopole antenna. This configurationallows to transmit a broad range of frequencies form DC to few GHz tothe antenna/tissue. The body of the ablation electrode 60 is configuredas a coaxial cable in the proximal section (FIG. 14B) which comprises acore ‘X’ surrounded by a dielectric 30 with the shield ‘X’ and an outerinsulator 35. The proximal section is insulated, in the distal end ofthe shield, e.g. few millimeters section, the insulator is removed,causing this section to acts as the ground plane 20 of the antenna. Thedistal section 15, is the positive of the antenna which is connected tothe core of the coaxial cable at the distal tip of just distal to theground plane of the antenna. The positive plane of the antenna comprisesa helical coil wound on an insulator/dielectric material but has nodielectric or insulation covering the outer surface of the helical coil.The helical coil has closely wound pitch, and each turn is separated bya dielectric 30. The width of the turns of the helical coil may beuniform throughout the length of the coil or may vary from proximal todistal; which can potentially affect the sensitivity of the antennaelectrode. In another configuration of the same design, the helical coilis replaced by a conductor wire or a tubing. The length of the helicalcoil and or the wire can vary from 2 mm to 15 cm. It can be straight,curved, shapeable or telescopic to adjust for different lengths andconfigurations. The ablation RF is delivered to the tissue from thepositive plane of the antenna-needle but can be applied from both, thepositive and the ground plane as well.

FIG. 14C provides an electrical schematic of the antenna electrode whenplaced in a tissue. The tissue behaves as a capacitor and resistor inseries. During the RF ablation procedure, as the dielectric propertiesof the tissue change, so do the reflection/transmission properties ofthe needle antenna electrode and the change used to quantify ablationzone and extent of thermal injury.

FIG. 15 shows a configuration for the RF ablation antenna needleelectrode 10 with the ground plane 20 located on the outer surface ofthe body. This increases the sensing signal penetration, as shown by thefield lines thru the entire thickness of the tissue (FIG. 15B and D).This is particularly useful for monitoring ablation of shallow lesions,not further out from the surface of the skin, where excessive ablationcan cause burn wounds close to the surface of the skin. The ground plane20 may be fixed to the electrode body or can be connected during theprocedure by an number of external fixation methods, such as screw onattachments, gripper chucks, gripper jaws, and the like. The groundplane may be a conductor on a flexible dielectric surface, e.g.polymeric or fabric which is glued to the skin by an appropriateadhesive which does not attenuate conductivity.

FIG. 16 shows an RF/microwave needle antenna electrode in one embodimentof the invention which is a combination of a monopole antenna and adipole antenna with the ground plane of the dipole antenna placedoutside the body. The body of the needle antenna electrode is a triaxialcable. This design has one positive 15 and two ground planes 20, oneground plane in close proximity to the positive and one ground outsidethe body. In one antenna electrode configuration, the core and the innershield form a monopole/modified dipole antenna. RF for ablation may bedelivered to the tissue by the positive plane/electrode or both thepositive and ground plane/electrode. The ablation zone is monitored byreflection measurements between the inner monopole/modified dipoleantenna and between the positive and the ground plane outside the body.As indicated by the field lines in FIG. 16B, this antenna configurationhas a wider sensitive region and can be used for shallow and deeperanatomical locations. This configuration provides distinct return loss,phase angle profiles in the frequency domain to monitor local tissuechanges between the two antenna combinations simultaneously. The outerground plane can be made in different forms as described earlier forFIG. 15 and need not be fixed to the needle antenna electrode. Since inthis configuration there are two antenna on a single device and tworeflection measurements are made, these can be made intermittently usingone or more reflection measurement setups. An analog or digital switchwill enable measurements with the two antenna intermittently.

FIG. 17 shows a schematic of the setup to monitor RF ablation zone withthe needle antenna electrodes described in FIGS. 14-16. This is done bymonitoring changes in magnitude and phase of incident and reflectionsignal, i.e. reflection properties of the needle antenna electrode, i.e.return loss, phase angle in the frequency domain, during the ablationprocedure. The ablation RF (500 KHz) generated by the RF generatorpasses thru a low pass filter to attenuate all non-ablation frequencies,a ground pad placed on the patient completes the ablation circuit. Thehigh pass filter prevents the ablation RF from entering the networkanalyzer and other measuring electronics, but allows the sensingRF/microwave frequencies to pass from and back to the network analyzer.The network analyzer measures and computes the difference in magnitudeand phase of the incident and reflected signal and computes the returnloss, phase angle, and the like, in the frequency domain during theprocedure and displays the information on the computer/user interface.

The electrical properties of these antenna electrodes is a function ofthe tissue in which the antenna electrodes are placed and the antennadesigns, i.e. number of turns, diameter, pitch, dielectric properties,length of the coil, spacing from the ground plane, and the like. As thetissue properties change during ablation, so do the characteristicresonant frequency/phase reversal frequencies, return loss profile andthe phase angle profiles. After the RF ablation antenna electrode isplaced in the tissue of interest under imaging guidance, the baselinereturn loss, phase angle and phase angle reversal frequency data isobtained. During ablation the changes to these characteristic propertiesis monitored and depth of lesion formed/ablation zone, rate of lesionformation is inferred and monitored. These devices will have limitationson depth assessment to a few mms 5-15 mm diameter based on change inresonant frequency changes. To further assess ablation zone, beyond thesensitivity offered by resonant frequency shift, other methods toestimate ablation zone based on total energy deposited are implemented.Namely, estimating the time duration and amplitude of RF energy(wattage) applied over the surface/volume of the tissue.

As described earlier, efficacy of RF ablation is a function of tissueproperties at the electrode-tissue interface. A corresponding safereturn loss, phase angle and resonant frequency conditions at which,there is minimal thermal tissue damage, is determined, and the ablationparameters adjusted to hold this state. This method can be used toensure no excessive thermal damage occurs to the tissue at theelectrode-tissue interface, e.g. charring, water boiling, and the like,which is needed in order to create deeper lesions. By titrating theinput RF power levels such that an optimum interface tissuecharacteristics is maintained to create deep lesions. The total energydelivered to the tissue in these controlled conditions is used toestimate the ablation zone, where the ablation zone is proportional tothe total energy deposited. However for this method to be effective, itis important to know if there are any blood vessels which will act asheat sinks.

This feature can be incorporated in the user interface depicted herein,where the physician sets the safe level of maximum resonant frequency orthe resonant frequency range and time duration of ablation in thatrange. The controller hardware and software adjusts/titrates the RFinput power applied by the RF generator to maintain the resonantfrequency range.

The methods described above implement monitoring the reflection (S11)electrical properties of an antenna electrode in the frequency domain tomonitor RF ablation procedure and assess lesion formation. One of thelimitations of these systems is the limited depth of penetration and canbe overcome by performing transmission measurements along withreflection measurements. Reflection measurements will be used to monitorrate of tissue property changes in contact to the RF applicator 10 andthe transmission electrical properties will be measured to quantifyablation zone and extent of tissue thermal damage in the volume oftissue being ablated.

FIG. 18 shows the schematic of a system of the invention which performstransmission (S12 and/or S21) and reflection (S11) measurements duringRFA procedures to assess ablation zone. The system comprises a needleantenna electrode 10 which is placed in the tissue to be ablated andreceiver coils 90 which are placed outside the body, e.g. on the surfaceof the skin. The needle antenna electrode may be a monopole/modifieddipole antenna and transmits an electromagnetic signal in the frequencydomain, which travels thru the tissue to the external receiver coils 90.S11 reflection measurement will provide assessment of tissue directly incontact with the electrode and the S12 transmission properties willprovide assessment of the tissue thru which the signal travels toquantify ablation zone and extent of thermal injury. The ground pad tocomplete the ablation RF circuit is a high impedance pad to prevent highfrequencies from coupling to it and getting grounded, or it has a lowpass filter inline to the RF generator to prevent high frequency signalsfrom being grounded.

Reflection electrical properties, e.g. return loss, phase angle,reflection coefficient, of the needle antenna electrode 10 will bemeasured in the frequency domain to assess tissue properties in contactwith the needle antenna electrode. The transmission electricalproperties between the needle antenna electrode and surface receivercoils, namely changes in amplitude and phase of the signal transmitted,before and during ablation are monitored to assess the ablation zone andextent of thermal tissue injury. The reflection and transmissionassessment is performed by a vector network analyzer capable of bothmeasurements. Also the transmitted signal can be measured by otherequipment, e.g. spectrum analyzer, which will measure the amplitude andphase of the signals received by the surface receiver coils during theablation procedure.

The receiver coil placed on the surface may be one or more receiverantenna coils, tuned to a broad frequency range. These can be simpleloop coils, phased array loop coils, spiral antenna arrays, and thelike. The signal received by these coils may be measured individually inintervals or as a combined output. Digital and analog switches enableselect the receiver coils to be monitored and the time intervals atwhich the signals to be processed. In case a spectrum analyzer is used,a separate signal generator with an output in a broad range offrequencies can be used to measure transmission properties to assesslesion formation and confirm ablation of cancerous tissue, and the like.

It is known that different tumors absorb electromagnetic signals atdifferent frequencies, e.g. breast cancer malignant tissue absorbs RF inthe range between 180-400 MHz, which may change with antenna design. Anelectromagnetic signal in this frequency range may be transmitted by theablation antenna electrode and the magnitude and phase change monitoredduring the ablation procedure will be used to ensure complete ablationof the tumor and the margin.

The receiver coils placed on the surface of the skin/body need to makegood electrical contact with the surface of the skin, so appropriateconductive adhesive will be required. These coils can be various typesincluding loop coils, archimedean spirals, and the like. The coils canbe single coils, arrays, phased arrays, and the like designed to receivethe high frequency signals transmitted by the ablation antennaelectrodes thru the tissue. The output of the receiver coils can beconnected to a network analyzer and/or a spectrum analyzer, via a switchwhere the signal from one or more coils at a time a received andprocessed.

FIG. 19 shows the schematic of an RF ablation lesion assessment systemof the invention implementing reflection and transmission measurementfor ablation of anatomies such as breast cancer tumor ablation. Duringbreast cancer tumor ablation procedure, a needle antenna electrode 10will be placed in the tumor, at a predetermined location, usingultrasound, MRI or guidance modalities (FIG. 19A). The needle antennaelectrode will be placed in the tumor such that the entire tumor can beablated in a single insertion, but may be with retracting the needle tocompletely ablate the resection zone. The placement of the needleantenna electrode in the anatomy with respect to the tumor is recorded(preoperative or intraoperative images) and ablation zone determined.Presence of heat conducting anatomies such as blood vessels, glands, andthe like is noted and recorded. External receiver coils 90, which arephased array coils will be placed around the breast, such that they arein good contact with the skin with minimal air pockets, which willaffect signal reception (FIG. 19B). The needle antenna electrode andexternal coils are connected to the high frequency measurementequipment, e.g. vector network analyzer, spectrum analyzer, and the likevia filter hardware (FIG. 19C). Baseline reflection transmissionproperties with the needle antenna electrode and surface receiver coilsis obtained and recorded, which may include return loss, insertion loss,magnitude and phase measured in the frequency domain. The amplitude ofthe sensing signal for reflection and transmission is typically lessthan 1 W. After the baseline properties are obtained, RF ablation isturned on and the power level is adjusted such that the resonantfrequency of the needle antenna electrode as measured by reflectionproperties is maintained in the safe mode not to cause excessivetemperature rise in the vicinity of the needle electrode, thus maximizethe ablation zone. The transmission electrical properties i.e. magnitudeand phase of transmitted signal from the needle antenna electrode to theexternal receiver coils is recorded in the frequency domain during theablation procedure. Preoperative ablation experiments will guide theablation lesion/zone determination based on the shift in maximuminsertion loss frequency and maximum return loss frequencies. Inaddition to the frequency sweep assessment, insertion loss in a narrowfrequency range may be measured since the breast cancer tumors and othertumors absorb EM radiation in a frequency range of 100-500 MHz (thisfrequency may change depending on antenna design). Change in insertionloss of these frequencies may imply complete tumor ablation. Similarmethods may be used to other ablations, e.g. nerve ablation for painmanagement, liver tumor ablation, and the like.

FIG. 20 shows the characteristic amplitude profile of the insertion lossbetween the signal transmitted by the needle antenna electrode 10 andreceived by the receiver surface coils 90 in the frequency range. Bymonitoring the frequency/frequencies of maximum insertion loss and phaseof the signal at the maximum loss frequency/frequencies; the ablationzone and extent of thermal injury is quantified. Return loss/logmagnitude v/s frequency indicating coupling between the ablation needleantenna electrode 10 and the sensing antenna 90 on the surface. Thedifferential in the coupling frequency from onset of ablation is used todetermine ablation zone diameters.

FIG. 21 shows a system setup in one embodiment of the invention whichcan be implemented to create, monitor and maximize ablation lesions bycontrolling RF power applied during ablation. The system utilizesmonitoring S11 reflection resonant frequency to continue ablating at asafe level and monitoring S12 transmission for assessing ablation zoneand extent of tissue damage. The physician sets the safe level ofablation, i.e. the maximum resonant frequency or the resonant frequencyrange in which to maintain the ablation power input and time duration ofablation. The controller hardware and software adjusts/titrates the RFinput power applied by the RF generator to maintain the resonantfrequency range.

During clinical use the operator will place the needle antenna electrodedevice 10 in the anatomical region of interest guided by intraoperativeor preoperative Mill, CT, X-ray or ultrasound imaging. Upon placing theneedle antenna electrode 10 in the desired anatomical target, the needleantenna electrode 10 is connected to the interface circuit comprising RFfilters, i.e. low pass and high pass filters, which are in turnconnected to the RF ablation generator, network analyzer (or signalgenerator and amplifier). The surface receiver coils 90 are carefullyplaced on the surface of the skin making sure they are in good contactand there are minimal air gaps between the body and the receiver antenna90, and connected to the network analyzer (or spectrum analyzer). Agrounding pad is placed in a region away from the ablation zone tocomplete the RF ablation circuit pathway and connected to the RFgenerator via a low pass filter.

Upon completing the setup, the baseline reflection transmissionmeasurements are performed and data is recorded. The safe ablationwindow in terms of resonant frequency range is set by the operator inthe manual mode or auto control mode, and RF energy is applied. Theinput RF power levels are regulated/titrated by monitoring the S11reflection properties of return loss, phase angle and resonantfrequency. The ablation zone is assessed by the reflection properties aswell as transmission properties (i.e. frequency and phase of maximuminsertion loss), and the ablation is stopped after desired ablationtarget is achieved or a steady state of reflection transmissionproperties is reached, i.e. ablation zone has reached a steady state.

FIG. 22 sets forth different configurations of antenna designs that canbe incorporated for needle antenna electrode configurations shown inFIGS. 14-21 in various embodiments of the invention.

FIG. 22A illustrates a loopless/monopole antenna with a straightpositive section.

FIG. 22B illustrates loopless/monopole antenna with a backward coiledhelical positive section.

FIG. 22C illustrates loopless/monopole antenna with a forward coiledhelical positive.

FIG. 22D illustrates a dipole with positive and ground plane co-wound.

FIG. 22E illustrates a solenoid antenna with a helical coil connectingpositive and the ground.

All the antennas from FIGS. 22A-E can be designed with a balun circuiton the shield as shown in FIG. 22F, which creates a high impedance andprevents the current leaking on to the shield; only the section of theshield distal to the balloon acts as the ground plane.

FIGS. 22G and H illustrate embodiments of the invention which include aslotted shield antenna and modification for an ablationantenna-electrode. The needle antenna electrode may be configured as aslotted shield antenna, with one or more slots 250 along the length ofthe ablation section of the electrode including coax cable 600. Theshield extends to the distal end of the antenna electrode, and somesections of the shield are not insulated to allow for electrical contactwith tissue. A coil 280 may be connected to the core of the coax thruthe slots in the shield and the coil 280 wrapped around the shield witha dielectric between the coil and the shield. Coil 280 is attached tothe core thru the slotted shield with no insulation being on coil 280which acts as the positive of the antenna electrode. There is adielectric under the coil over the shield to prevent direct electricalcontact. Ablation RF is applied to both the core and the shield. Withthis design, the sensitive section of the antenna is in the middle ofthe ablation zone, and provide better assessment of the extent ofablation zone.

Different configurations of the cardiac RF ablation catheter antennaelectrode of the invention are described below. Since the ablationantenna electrode has positive and ground planes of the antennaeincorporated on the surface of the electrode in close proximity, thebase of the antenna electrode is constructed out of dielectricmaterials. These can be polymeric materials, such as but in no waylimited to polyether ether ketone (PEEK), polyimide, ceramic materials,such as alumina, aluminum nitride, and the like. These materials havepoor electrical conductivity (very high electrical resistivity) and lowdielectric constant (dielectric constant <20), to impart electric andmagnetic field penetration in the medium surrounding the antennae.During the ablation procedure, as tissue in contact with the electrodeheats, this thermal energy is conducted to the electrode as well,causing the electrode to heat. Electrode temperatures over 43° C. cancause blood coagulation on the surface of the electrode causing highimpedance to RF current, preventing tissue ablation. To avoid bloodcoagulation on the electrode, the electrode needs to be cooled during RFablation. This is achieved by closed loop saline irrigation or openflush saline irrigation. Open flush saline irrigation is preferred dueto its relatively better temperature control due to constant salineflow, which also maintains the tissue surrounding the electrode cool,thus potentially increasing lesion depth.

FIG. 23 shows a configuration in one embodiment of the invention of amodified coaxial antenna electrode. The positive of the antennaelectrode 15 is in the center of the distal surface of the electrode andis about 2-50% of the electrode surface area. The positive 15 isseparated from the remaining electrode surface by dielectric 30 wherethe rest of the surface area of the electrode acts as the ground planeof the electrode 20. The distal hemispherical surface of the antennaelectrode is the sensitive region of the electrode is as shown by thefield lines in FIG. 23D. The outer surface on the whole, or in part, maybe coated with a metallic conductive layer and will function as theground plane 20 of the antenna electrode 10. This coaxial antennaelectrode is sensitive only on the distal surface of the electrode andlacks sensitivity on the sides primarily due to the presence of theground plane and the field lines from the positive will couple only tothe ground plane on the hemispherical side. The ablation RF for thecoaxial antenna electrode for this embodiment is delivered to the tissuefrom the ground plane of the antenna electrode, so the low pass filtercircuit will be connected to the shield side of the cable, as opposed tothe core.

FIG. 24 shows a coaxial antenna electrode of the invention withsensitivity on the sides. The positive of the antenna 15 has nodes onthe side of the cylindrical side of the electrode to provide sensitivityto the distal spherical surface and the cylindrical side surface(similar to the slotted shield antenna embodiment). One of more positivenodes 15 can be located on the sides separated from rest of the groundplane 20 by a dielectric section 30. This imparts sensitivity to thesides of the electrode so that RF ablation can be monitored from allsides of the electrode. The five positive nodes, for reflectionproperties measurement may be connected to a single coaxial cable oreach to an individual coaxial cable with a common ground plane, or eachto a cable with five cores and a common ground shield. The output ofeach node may be monitored simultaneously or intermittently. Forintermittent measurement, each node may be routed via a digital/analogswitch to facilitate measurement and recording the reflection S11properties in the frequency domain.

FIG. 25 shows a coaxial antenna electrode of the invention with a spiralon the ground plane on the hemispherical surface. The positive plane 15is separated by a dielectric 30 from the ground plane 20. The groundplane is configured as a spiral 50.

One of the limitations of the coaxial sensor with one node or multiplesnodes as described in FIGS. 23 and 24 is that the return loss profilewill be fairly flat in the frequency domain and there is not a distinctresonant frequency/phase reversal frequency to track during the ablationprocedure, affecting the sensitivity and specificity of measurements. Inorder to create a distinct resonant frequency the coaxial sensorsdescribed in FIGS. 23 and 24 can be configured with a spiral structure50 in the ground plane 20 adjacent to the positive nodes 15 as shown inFIG. 25. The spirals 50 in the ground plane 20 are connected to theground plane 20 from the outside of the spiral and the inner end of thespiral is left open. This adds inductance to the electrode ground plane,thus creating a resonance frequency which can be monitored and trackedduring the procedure. For the coaxial antenna electrode designs theablation RF is delivered from the ground plane of the electrode, but thesensing RF is transmitted from the core or the positive of the antennaelectrode.

FIG. 26 shows the coaxial antenna electrode of the invention withpositive nodes 15 on the cylindrical side of the electrode, with theground plane 20 configured as a spiral ground plane 50 around thepositive node 15. This configuration imparts sensitivity to the sides ofthe electrode and a characteristic resonant frequency to monitor duringablation procedure. The positive nodes may be connected to one or moreindividual conductors in a single common ground cable configuration. Thespirals on each side may have different number of turns, spacing andstrut thickness to provide different electrical characteristics, toenable identify electrode-tissue contact orientation.

FIG. 27 shows an antenna electrode configuration of the invention, wherethe positive of the antenna electrode 15 on the hemispherical surface isconfigured as a spiral-helix where the positive 15 of the antenna is ahelix-spiral 40, each turn is separated by a dielectric 15 and theentire helix-spiral is surrounded by the ground plane 20 on the distalhemispherical surface of the electrode. This creates field lines asshown in FIG. 27E and potentially increases field penetration in thetissue. The ground plane extends on all the sides of the antennaelectrode assembly and continues to the proximal end for connecting tothe coaxial cable. The spirals in the positive plane 40 can beconfigured in one or more layers, each spiral layer is separated by adielectric layer and can be arranged one over the other wound in same oropposite directions to increase the penetration or sensitivity of theantenna electrode.

FIG. 28 shows a spiral helix antenna electrode of the invention with oneor more positive nodes 15 on the sides of the electrode as well as onthe hemispherical surface, where the positive 15 of the antenna isarranged as a spiral-helix 40 on the sides of the cylinder and thehemispherical side. This antenna electrode design imparts sensitivity todistal hemispherical surface as well as to the sides of the electrode.Ablation RF may be delivered to the tissue by the positive plane 15 orthe ground plane 20 or both the positive plane 15 and the ground plane20. The low pass filter will be configured to attenuate non-ablatingfrequencies on the core and the shield accordingly. Spiral antennaelectrode with multiple positive nodes on the side; with spiral on thecore/positive on the sides. Each positive node may be connected to thesame coaxial cable core (positive) or to different coaxial cables, or toa single shielded cable with multiple cores or a multilayer cable(triaxial cable, quadaxial cable, and the like).

FIG. 29 shows an embodiment of the invention in which the antennaelectrode has the positive of the antenna 15 configured as aspiral-helix 40 and the positive of the antenna 15 on the distalhemispherical surface is a helical-spiral surrounded by a ground plane20 with a gap in the circumference. The positive helical spiral 40continues out of the hemispherical surface in this gap in the groundplane and continues as a helix on the sides of the electrode where thepositive 15 is co-wound helically with the ground plane 20. Thisstructure provides sensitivity to the entire electrode including thesides. This antenna structure attributes distinct electrical propertiesdue to the helical spiral on the distal hemispherical surface andhelical coil antenna structure by the co-wound positive plane and theground plane spirals on the sides; this enables to characterizeorientation of the antenna electrode as it is in contact with the tissueand assess lesion formation.

FIG. 30 shows a spiral helical antenna of the invention with twoantennae structures; one connected to the distal hemispherical spiralhelical antenna and the other connected to the helical coil dipoleantenna on the side of the electrode. Both antennae may have one commonground or separate ground planes. Each antennae may be connected by oneor more coaxial cables or triaxial cable. On the distal hemisphericalsurface positive of the antenna 15 coiled in a spiral surrounded by theground plane ring 20. On the sides of the electrode, a positive node 15is connected to the core of the coaxial cable (as the positive plane 15on the distal hemispherical surface) and is coiled in a helix to form ahelical antenna. A common ground plane 20 is on the circumference of thedistal hemispherical surface and the circular side edge of thecylindrical side of the electrode. On the cylindrical side, the groundplane is under the helical positive plane and the two are separated byan insulator/dielectric layer. This antenna electrode structure issensitive on the sides of the electrode and on the distal hemisphericalsurface.

FIG. 31 provides yet another embodiment of the antenna electrode designin which the positive 15 is configured as a spiral helix which starts onthe distal hemispherical surface, then continues on the side for somedistance. Separated by a dielectric 30 is a circular ground plane 20. Asimilar design where the positive spiral helix starts on the sides andends on the hemispherical surface can be implemented. This antennaelectrode has sensitivity on the distal hemispherical surface and thesides of the electrode. The pitch, turns and width of the spiral strutsand gaps in the spiral struts can be configured to provide a fairlyisotropic sensitivity region. This design could be modified byco-winding the ground plane with the positive helical coil on the sidesof the electrode in a preferred embodiment.

In another configuration of the spiral helix embodiment, the positiveand the ground of the antenna are co-wound in an Archimedean spiralhelical coil configuration on the hemispherical surface and the sides ofthe electrode. The positive of the antenna 15 and the ground of theantenna 20 are co-wound in a spiral in the hemispherical section of theelectrode and then as a co-wound helix on the sides of the antenna.Alternate designs would include, one where both the ground and thepositive/core are connected to the coaxial cable at the distal tip; orthe core is connected at the distal surface and the ground is connectedto the shield at the proximal end.

FIG. 32 shows an electrode of the invention which is configured in atriaxial design with the inner core and the first/primary shield layerbeing incorporated in the electrode forming one antenna, and theprimary/first shield and the second shield forming the other antenna.Each antenna can have the positive or the ground/shield in a coiled,singular meandering configuration.

FIG. 33 depicts an embodiment of the invention wherein the antennaelectrode is a solenoid coil antenna with a spiral-helix combination.The core of the coaxial cable is connected to the solenoid spiral-helixcoil at the distal hemispherical surface (at the center). The positiveof the antenna is then coiled in a spiral on the distal hemisphericalsurface of the electrode and then continues as a helix along the sidesof the electrode-antenna and connects to the ground plane via acapacitor less than 200 pF to block the ablation RF from entering theshield. This capacitor can be placed on the ground plane at otherlocations as well. This antenna electrode exhibits different resonantcharacteristics in response to the RF progression. On onset of ablation,the return loss at the resonant frequency gradually increases andflattens to zero as the lesion progresses. The capacitor blocks theablation RF from going on the ground plane and tunes to a desiredfrequency.

FIG. 34 depicts an embodiment of the invention having two loop coilantennae electrodes in a quadrature arrangement. The antenna traces onthe distal surface can be spiraled to provide resonance or add to theinductance. These antennae can be saddle coils with an overlappingsection and other antenna configurations. With these antennae coilelectrodes ablation assessment can be carried out in S11/S22 reflectionmode and S21/S12 transmission mode simultaneously. Other coilconfigurations with similar arrangements can be envisioned, e.g. withcoiled traces, zig-zag traces, co-wound/coiled traces, traces inopposite directions, and the like to increase connecting field lines andcoupling. Each coil may be connected by separate coaxial cables; or atriaxial cable with common ground conductor.

In the various embodiments described herein, the ablation antennaelectrode of the invention having positive and ground planesincorporated on the surface of the electrode in close proximity, thebase of the antenna electrode is constructed out of dielectricmaterials. These can be polymeric materials, e.g. polyether ether ketone(PEEK), polyimide, and the like, or ceramic materials, such as alumina,aluminum nitride, and the like, which have poor electrical conductivity(very high electrical resistivity) and low dielectric constant(dielectric constant <20), to impart electric and magnetic fieldpenetration in the medium surrounding the antennae. During the ablationprocedure, as tissue in contact with the electrode heats, this thermalenergy is conducted to the electrode as well, causing the electrode toheat. Electrode temperatures over 43° C. can cause blood coagulation onthe surface of the electrode causing high impedance to RF current,preventing tissue ablation. To avoid blood coagulation on the electrode,the electrode needs to be cooled during RF ablation which is achieved byclosed loop saline irrigation or open flush saline irrigation. Openflush saline irrigation is preferred due to its relatively bettertemperature control because of the constant saline flow, which alsomaintains the tissue surrounding the electrode cool, thus potentiallyincreasing lesion depth.

In various embodiments, the ablation electrode base component isfabricated out of ceramics or polymers, or composite constructioninvolving metal and dielectric layers with lumens for saline flush. Theantenna structures are then build on this dielectric base structure. Thebase part comprises a cylindrical electrode base structure with ahemispherical distal surface to provide smooth contact with the tissueto be ablated. As shown in FIG. 35, saline flush lumens are fabricatedto provide open saline irrigation. The saline flow is induced by a pumpplaced externally (typically a closed loop with the RF ablationgenerator so that the pump turns on when RF is applied) and delivered tothe electrode via saline flush input ports. A thru lumen in the centerprovides access to connect the coaxial cable to the positive of theantenna. The ground plane of the antenna extends thought out the outersurface of the base component where the coaxial cable is connected. Thedistal surface and the side are typically in contact with the electrodeto deliver ablation RF into the tissue.

The antenna electrode is fabricated in multiple steps/stages; initiallya base structure out of a dielectric is machined or fabricated. Thesaline flush lumens, lumen to connect the positive of the antenna andthe ground plane to the coaxial cable provided. Ports and lumens tohouse the thermocouple, positive plane nodes, and the like will beincorporated in the base structure. The ground plane and the positiveplane components are then created on the substrate of conductivebiocompatible metals, e.g. gold, SS316, and the like, by various means.

In one method the conductive elements of the antenna are sputtered,coated. In another method they are fabricated, machined, cast, orelectrodeposited and then assembled on the ceramic/polymeric base. Opensaline flush irrigation are utilized to cool the electrode and adjacenttissue during ablation. Since saline is a conductive solution (due toNa+ and Cl− ions) flowing saline solution can act as a long conductingwire and induce noise in high frequency measurement. To overcome this,the inner surfaces of the saline flush lumens have a dielectric coatingand the exit ports on the surface of the electrode have a dielectric rimaround them. This prevents direct saline contact with the conductivesurfaces when held against the tissue.

With reference to FIG. 35, the antenna electrodes are then assembled ina steerable catheter body 700 which includes a braided tubing withvarying stiffness, and a pull wire anchored in the distal section andconnected to the actuation mechanism in the handle section at theproximal end to enable deflect and steer the catheter in desiredorientation. A fiberoptic temperature sensor 570 or a thermocouple isembedded in the electrode and bonded with thermally conductive butdielectric adhesives. Similarly the tubing to deliver saline flush 550to the electrode are connected/bonded to the proximal end of theelectrode. The core of the coaxial cable 600 is connected to thepositive of the antenna via a hypotubing subassembly which runs in theelectrode central lumen and the shield is connected to the ground planeand may be crimped to the ground plane structure. The entire electrode,thermocouple, potentially contact force sensing structures areincorporated in the steerable catheter then connected to a connectorcomprising pins for thermocouple and other sensing electrodes and acoaxial connector for the ablation electrode. The system is ready foruse after appropriate sterilization processes.

In another embodiment as shown in FIG. 36, the spiral antenna electrodemay be deposited on a balloon 800 of a balloon catheter. The circuit maybe deposited directly on the balloon by sputtering or chemical vapordeposition methods; or fabricated and bonded to balloons. Duringclinical use the balloon may be advanced to the location of therapy,dilated with a fluid medium, e.g. oil, fat, gas, to open the balloon andto position the antenna electrode structure against the tissue to beablated.

In another embodiment as shown in FIG. 37,intramyocardial/transendocardial injection catheters are used to delivertherapeutics to the cardiac tissue, e.g. warm saline for ablation, celltherapies, ablative agents, simultaneously injecting warm saline andablation RF for creating deeper ablation lesions, and the like. Theantenna electrodes can be modified by incorporating a central lumen tohouse the injection needle. The needle may or may not be electrically apart of the antenna electrode. It may be inductively or capacitivelycoupled to the antenna electrode.

As shown in FIG. 37, the catheter includes a proximal section made ofstiffer braided tubing for imparting longitudinal stiffness, and asofter distal section. A pull wire runs along the length of thecatheter, to enable deflect the distal section. The distal end of thepull wire is anchored towards the distal end of the distal section ofthe catheter. At the proximal end, the pull wire is fixed to theactuator in the handle section. The actuation mechanism moves thecatheter body with respect to the pull wire deflecting the softer distalsection of the catheter.

The antenna electrode design for use with an intramyocardial injectioncatheter is shown in FIG. 37 also. A central needle lumen in theelectrode houses the needle, at the proximal end of the electrode, thecentral lumen is connected to a polymeric nonconductive tubing whichruns along the length of the catheter and houses the needle. The needleis a composite metal-polymer tubing, with the distal 0.5-2 cm of theneedle being metallic and the remaining length being a non-conductivematerial, e.g., polymeric. This is so that, the needle and the tubingare not a part of the antenna and do not influence return loss and phaseangle measurements. The inner surface of the needle may be coated with apolymeric layer to prevent direct saline contact and prevent electricalconductivity of the saline from affecting antenna properties. The needletip position with respect to the distal tip of the catheter can bemanipulated by moving the needle at the proximal end of the catheter.

During an intramyocardial injection procedure, the catheter will beadvanced into the cardiac chambers via suitable vascular access usingimaging guidance. The distal tip of the catheter is placed opposed tothe tissue so that the distal surface of the antenna electrode is incontact with the myocardial wall. This will be confirmed by monitoringthe return loss, phase angle and resonant frequency of the antennaelectrode. After the catheter tip is positioned at the location againstthe tissue, as confirmed by the return loss, phase angle resonantfrequency, the needle is advanced out of the catheter and catheter-wallcontact is ensured. When needle placement in the tissue and depth ofneedle in the tissue is confirmed, a contrast test injection may bedelivered. The therapy/injectate is then delivered into the myocardium,and depending on the electrical properties of the injectate, theinjection in the wall can be confirmed by changes in return loss, phaseangle profiles of the antenna electrode. The intramyocardial injectioncatheter with antenna electrode may be used to simultaneously perform RFablation and inject saline or other injectate at the same time usingmonitoring techniques described earlier.

The antenna electrodes implemented in cardiac RF ablation catheters andintramyocardial injection catheters as disclosed herein, can be modifiedfor use in MRI environment to enable MRI guided procedures with design,material and layout changes. The antenna electrode will be configured asa receive-only or transmit-receive coil by matching tuning of theantenna electrode to the MRI's Larmor frequency.

Since MRI involves obtaining signal from the hydrogen proton in watermolecules, interventional devices are not conspicuous in MRI.Transmit-receive or receive only antennae may be incorporated in thedevices to render them conspicuous in MRI. For use in MRI, all theantennae will be tuned to the Larmor frequency of MRI, e.g. 64 MHz for1.5 Tesla field strength, 128 MHz for 3 Tesla field strength. Thisenables the antennae to receive or transmit-receive NMR signal generatedby the hydrogen proton during a scan. These signals picked up by theantennae are transferred to the scanners receiver amplifiers via aninterface circuitry, which includes a matching tuning and decouplingcircuitry. The MRI scanner's signal processing system displays thesesignals into images which are then seen on the scanner consoles.

The static magnetic field and RF fields generated during MRI imagingprocess pose significant safety hazards and interventional devices needto be designed to make them safe for use in MRI. To make the devicessafe for use in MRI's static magnetic field environment, the cathetersand its components are fabricated out of non-ferromagnetic/magneticmaterials. This eliminates the undue/undesired mechanical forces beingexerted on the catheters due to the static magnetic field, which couldpose hazards to the patients and the operators.

During MR imaging, in order to obtain an image, the subject/patient issubjected to intense RF fields at Larmor frequencies, e.g. 64 MHz for1.5 Tesla and 128 MHz for 3 Tesla. This applied RF induces localelectric fields in the patient's body. An interventional device having along linear metallic/conductive component, when placed in this electricfield couples to the E-fields, voltage is induced in the device, whichin turn drives a current which is deposited in the tissue in contactwith the device, typically at the ends of the device, causingirreversible thermal injury. To render interventional devices safe inMRI the long linear components of the catheters/devices need to bereplaced with nonconductive polymeric or ceramic components. If longmetallic components are required, they need to be designed in a way toimpart high impedance at MRI's Larmor frequencies.

For the RF ablation catheters and intramyocardial injection catheters ofthe invention, the long linear components which will pose MRI safetyrisks are the pull wire, coaxial cables, wires which connect to theablation antenna electrode, sensing electrodes and the braiding in thecatheter body. The coaxial cables may be arranged with intermittentchokes or windings such that the impedance on the shield of the woundcoaxial cables exceeds 50 ohms/cm at Larmor frequencies when measured bya common mode measurement. The diameter, pitch and turns of the coaxialcable chokes can be adjusted to obtain this impedance. In embodiments,one or more coaxial cable chokes will be incorporated along the lengthof the catheter; typically the length of each choke will be shorter than10 cm for 1.5 Tesla and 5 cm for 3 Tesla field strengths to minimizecoupling to local E-fields. The length of the chokes, diameter and pitchshould be adjusted so as to get over 300 ohms impedance over the entirelength of the choke, but keeping the overall length shorter than 9 cmfor 1.5 T and 4.5 cm for 3 T field strengths. The overall length of thecoaxial cables will typically be an odd multiple of λ/4 (quarterwavelength) for ease of decoupling by a pin diode.

FIG. 38 illustrates a braided section of catheter tubing in oneembodiment of the invention. The metal braiding used in catheter tubingincludes two or more flat or round wires braided in sets of two suchthat wires crisscross and overlap one over the other, creating a thickweave and impart longitudinal column strength, rigidity and longitudinalflexibility at the same time. Such a braided wire structure acts as along linear conductor, since all the wires are electrically connectingeach other on every wind, posing significant RF safety risks when usedin MRI. To make the braided section of the catheter safe for use in MRI,a braiding with 2 or more wires where at least half the number of wireshave an insulating/dielectric coating on them to prevent electricalcontact with each other, are wound/braided with pitch and diameter suchthat each individual wire in a braided section will have an impedanceexceeding 25 ohms/cm at the Larmor frequency when measured in the commonmode. Further, in a length shorter than quarter wavelength for a barewire, i.e. shorter than 10 cm for 1.5 T and 5 cm for 3 T, an individualbraided wire will have an impedance peak exceeding 300 ohms at Larmorfrequencies, i.e. 64 MHz for 1.5 T and 128 MHz for 3 T. No wires in thebraid are in direct electrical contact with each other and the overallassembly is insulated in a dielectric coating. The insulating coatingcould be varnish, lacquer, polyimide and other polymers. Another method,would be to create a dissipative shield, where a section of the braidingmay be completely uninsulated, so that it is in direct contact withtissue. This dissipates the induced currents over a large surface areacausing minimal tissue thermal injury.

FIG. 39 illustrates an MRI active cardiac ablation catheter of theinvention. The catheter includes an antenna electrode, connected to acoaxial cable with one or more intermittent chokes to transmit and/orreceive NMR signals. The catheter includes a wire with multiple RFsuppression chokes for transmitting ablation RF or a polymeric tube tohouse the injection needle. The assembly is housed in a metallic braidedtubing or a polymeric tubing; where each braid wire is individuallyinsulated and the braid wires arrange in a pitch and diameter such thateach wire has an impedance over 50 ohms at NMR frequencies. Alternatelyan entirely polymeric steerable catheter may be implemented as well. Anon-polymeric pull wire enables deflect the distal section and steer andtorque. The match and tune circuit interfaces the output of the antennato scanner receivers frequencies and can be incorporated in the distalsection close to the antenna electrode or in the proximal handle sectionof the catheter. Since, it is known that tissue under ablation changeselectrical properties during the ablation processes; differentmatching-tuning strategies can be implemented so that the electrode MRIsignal changes with tissue contact, RF delivery to tissue and lesionprogression. Auto tuning approaches may be implemented; which may betterenable monitor and assess lesion formation. Monitoring reflectionelectrical characteristics of the antenna-electrode by a networkanalyzer during RF ablation can be done by filtering out all frequencieslittle over the Larmor frequency.

FIG. 40 illustrates an MRI active injection catheter of the invention.The antenna electrode 10 is connected to a coaxial cable with one ormore intermittent chokes, where each choke has an average impedance ofover 50 ohms/cm when measured on the shield in the common mode at MRIfrequencies. The center of the electrode is connected to a polymerictubing which houses the injection needle assembly. The injection needleassembly may be permanently incorporated in the catheter or may beremovable to function as a guidewire lumen to facilitate advancing thecatheter in the left ventricle. The needle is a composite needle, wherethe distal 0.5 to 2 cm of the needle is made of an MRI compatible metaland rest of the length is made of a polymeric tube; this is to preventthe needle component from acting as an MRI antenna and confounding thesignal. The conductive end of the needle may be in direct electricalcontact with the antenna electrode so as to visualize the needle in theMRI image as it advances out of the catheter and retracts back in thecatheter.

During use in MRI, the intramyocardial injection catheter, the ablationcatheter and other needle-electrode catheters may be used in combinationwith other external coils to receive NMR signals. Since these cathetercoils will be connected to separate receiver channels, the signals fromthese devices may be color coded to make the devices conspicuous in MRIand trackable as well.

FIG. 41 is a schematic of a layout using the antenna electrode cathetersfor microwave ablation. The ablation catheter with the antenna electrodeis connected to a signal generator, which generates an electromagneticsignal in a narrow band or a broad frequency range which may remainconstant during the ablation procedure or change as the ablationprogresses. The output of the signal generator is amplified by theamplifier and the directional coupler measures the amplitude oftransmitted and reflected frequencies to and back from the antennaelectrode. A controller may be implemented to adjust the ablation signalfrequency as the ablation progresses so as to minimize reflected energyand deposit maximum energy in the tissue to create deeper necroticlesions. Since microwave energy ablation is not based on ohmic heating,as like low frequency RFA, adjusting the input frequency to match theantenna electrode's resonant frequency, will enable deposit more energyin the tissue. This will be safer, since ablation can be carried out atlower power levels.

FIG. 42 is a schematic of a thermoacoustic imaging system, wheremicrowave energy pulse of a short duration may be delivered alongsidelow frequency RF current. A high frequency microwave pulse over 900 MHzfrequency will generate acoustic noise in the tissue. This acousticnoise may be intercepted by intracardiac or external ultrasoundtransducer devices, e.g. intracardiac ultrasound imaging and sensingcatheter, transesophageal catheter, and the like. Signal processingalgorithms will analyze the thermoacoustic signals to distinguishbetween ablated and non-ablated tissue.

Although the invention has been described with reference to the aboveexample, it will be understood that modifications and variations areencompassed within the spirit and scope of the invention. Accordingly,the invention is limited only by the following claims.

1. A device for assessing the state of a biological tissue comprising:at least one antenna configured to: i) transmit and receive assessmentsignals having frequencies of at least 1 MHz to and from the tissue; andii) transmit an ablation signal to the tissue; and a high frequencyoutput configured to output the received assessment signal to a networkanalyzer and signal processing device.
 2. The device of claim 1, furthercomprising a high frequency input configured to receive the transmittedassessment signal from the network analyzer and signal processingdevice.
 3. (canceled)
 4. The device of claim 1, wherein the ablationsignal has a frequency of 1 MHz or less.
 5. The device of claim 1,wherein the ablation signal has a higher wattage than the assessmentsignals.
 6. The device of claim 1, further comprising a low frequencyinput configured to receive the ablation signal from an ablationgenerator.
 7. The device of claim 1, wherein the at least one antenna isfurther configured to receive a DC signal from the tissue.
 8. The deviceof claim 7, further comprising a low frequency output configured tooutput the received DC signal to the network analyzer and signalprocessing device.
 9. The device of claim 1, wherein the at least oneantenna comprises a coaxial antenna comprising at least two electrodesseparated by a dielectric.
 10. The device of claim 1, wherein the atleast one antenna comprises a spiral antenna comprising: an innerelectrode wound as a spiral; an outer electrode surrounding the outsideof the spiral; and at least one dielectric separating turns of thespiral and separating the inner electrode and the outer electrode.11-18. (canceled)
 19. A method for determining a property of a tissue,the method comprising: transmitting, with at least one antenna of acatheter, a transmitted assessment signal having a frequency of at least1 MHz to tissue; receiving, with the at least one antenna, a receivedassessment signal having a frequency of at least 1 MHz from the tissue;detecting, with a processor of a network analyzer and signal processingdevice, an electrical property of the received assessment signal; anddetermining, with the processor, a property of the tissue based on thedetected electrical property of the received assessment signal.
 20. Themethod of claim 19, further comprising generating, with a signalgenerator of the network analyzer and signal processing device, thetransmitted assessment signal
 21. The method of claim 19, furthercomprising generating an ablation signal and transmitting, with the atleast one antenna, the ablation signal to the tissue.
 22. The method ofclaim 21, wherein the ablation signal has a frequency of 1 MHz or less,or a higher wattage than the assessment signals. 23-24. (canceled) 25.The method of claim 19, further comprising: receiving, with the at leastone antenna, a DC signal from the tissue; and analyzing, with theprocessor, the DC signal to determine an endocardial potential of thetissue.
 26. The method of claim 19, wherein determining the property ofthe tissue comprises performing a reflection S11 measurement on thereceived assessment signal, performing a transmission S21 or S12measurement on the received electrical signal, or a combination thereof.27. The method of claim 19, wherein: the detected electrical property ofthe received assessment signal is indicative of a change in anelectrical property of an antenna of the catheter; and determining theproperty of the tissue comprises inferring a change in a property of thetissue corresponding to the change in the electrical property of theantenna.
 28. The method of claim 19, wherein the property of the tissuecomprises an electrode-tissue contact quality, a rate of ablation, adegree of ablation, a temperature, a progression of lesion formation, anextent of lesion formation, a thermoacoustic image, or a combinationthereof.
 29. (canceled)
 30. An ablation device comprising: at least oneantenna configured to transmit and receive assessment signals havingfrequencies of at least 1 MHz to and from tissue; and a high frequencyoutput configured to output the received assessment signal to a networkanalyzer and signal processing device, wherein the at least one antennais further configured to transmit an ablation signal to the tissue, andwherein the ablation signal has a frequency of 1 MHz or less.
 31. Thedevice of claim 30, further comprising a high frequency input configuredto receive the transmitted assessment signal from the network analyzerand signal processing device.
 32. (canceled)
 33. The device of claim 30,wherein the ablation signal has a higher wattage than the assessmentsignals. 34-37. (canceled)